1. FIELD OF THE INVENTION
The present invention relates to an image signal processing device having a solid state image pick-up element such as a CCD (charge coupled device), particularly for reproducing a still picture.
2. DESCRIPTION OF THE PRIOR ART
In this kind of image signal processing device, the image is formed on and stored in the solid image pick-up element as a photoelectric charge and the photoelectric charge stored in the solid image pick-up element is read and recorded in a recording device, such as a magnetic tape or a magnetic disc in the recording mode, the image signal stored in the recording device is transferred to a monitor such as TV in the reproduction mode. However, in such a conventional device, the magnetic tape or the magnetic disc is used as the recording device, and it is necessary to choose a relatively low speed for recording the signal in the recording device or for reading the signal from the recording device.
On the other hand, a high speed image signal is needed for a monitor such as a TV. Consequently, in a conventional device uses a memory device in the recording mode, the photoelectric charge for one picture from the solid image pick-up element is transferred to the memory device and the signal transferred to the memory device is delivered to the recording device at a low speed. In the reproducing mode the signal for one picture is read from the recording device at a low speed, stored in the memory device, and the signal for one picture stored in the memory device is delivered to the monitor at a high speed.
However, this has required a memory device of large capacity, because the signal for one picture has to be stored, while it is difficult to reproduce a still picture which is stable for a long time.
This is, where a still picture is continuously reproduced, the signal stored in the memory is repeatedly read at high speed and delivered to a monitor such as a TV. On the other hand, where the signal is continuously read with the memory device, the increase of dark current or imperfect transfer efficiency makes it impossible to obtain a stabilized picture unless the content of the memory device is refreshed a predetermined intervals. Thus, it becomes necessary to transfer the image signal for one picture from the recording device to the memory at intervals. This creates the danger of distributing the whole picture with the refresher operation.
Further, even if the information of the picked up image for one field is repeatedly reproduced via the memory, the image resolving power is lowered, because the TV monitor scans two fields in one frame. Further, where the image continuously picked up for two fields is repeatedly reproduced, the picture is disturbed for every one field and the quality of the picture is degraded.